The present invention relates to a laser oscillator having a vacuum vessel, and more particularly to a shape of a vacuum vessel for use in a laser oscillator.
FIGS. 1(a) and 1(b) are schematic diagrams illustrating a cross-sectional side view and a cross-sectional front view of an example of a laser oscillator which has been disclosed in Published Unexamined Japanese Patent application No. 62-224990, respectively.
In FIGS. 1(a) and 1(b), reference numeral 1 designates a metallic enclosure which forms a vacuum vessel in which a laser medium gas is sealed; 2, a supporting frame disposed at the bottom of the vessel 1; 3, a heat exchanger which cools the laser medium gas; 4, an air blower which circulates the laser medium gas through a gas duct 6 serving as a passage; 5, a pair of electrodes facing each other; 7a and 7b, brackets mounted on the top of the vessel 1, respectively; and 8a, 8b and 8c, guide bars, the guide bars 8a and 8b being attached to the brackets 7a and 7b, respectively.
Supporting plates 9a and 9b which are made of aluminum or copper, are supported by the guide bars 8a, 8b and 8c. The plates 9a and 9b are provided with a half reflection mirror 10 and a total reflection mirror 11, respectively. Reference numeral 12 designates a pair of metallic bellows which connect between the vessel 1 and the support plates 9a and 9b respectively, while 13 denotes a laser beam.
In laser oscillation using a laser oscillator as constructed above, the air blower 4 is first actuated to produce a laser medium gas flow in a direction indicated by an arrow so that the gas flow circulates in the passage formed by the space between the pair of electrodes 5, the gas duct 6, and the heat exchanger 3 in this order.
Next, a high voltage is applied across the pair of electrodes 5 to generate a discharge, so that a laser medium gas is excited to emit a light having a wavelength of, in the case of CO.sub.2 for example, 10.6 m. This light in turn is amplified with an optical resonator constituted by the total reflection mirror 11 and the half reflection mirror 10 until it is released as a laser beam at the half reflection mirror 10.
To obtain a stable laser output in this process, the variations in the angle and position of the reflection mirrors (10) and (11) constituting the resonator have to be minimized. Amber or other material having a small value of linear expansion coefficient is employed as a material for the guide bars 8a, 8b and 8c supporting the support plates 9a and 9b to which the reflection mirrors 10 and 11 are fixed.
In laser oscillation, it is necessary to provide a prescribed insulation distance A between the electrodes 5 and the vessel 1 as shown in FIG. 1(a) because a high voltage is applied between the paired electrodes 5.
Because the pressure of laser medium gas at time of laser oscillation is as low as approximately 1/10 of the atmospheric pressure, the insulation distance A is set to a relatively large value. If the prescribed insulation distance A cannot be secured, a discharge may occur between the electrodes 5 and the vessel 1 resulting in the generation of heat and burning at the discharging portion. Besides, undesired gas such as a hydrocarbon (HC) or other volatile gases, which in turn may deteriorate the laser medium gas may be generated at the heated portion. In the case where, for example, a carbon dioxide gas (CO.sub.2) is employed as the laser medium gas, a chemical reaction of CO.sub.2 and the above-mentioned HC decreases CO.sub.2, resulting in a trouble of decreases in the laser oscillation efficiency. To guard against this trouble, the enclosure 1 is elongated vertically to secure the insulation distance A.
Note that this insulation distance A must be 50 mm or more usually, although it depends on the laser medium gas pressure, its composition, the shape of electrodes, their material, and voltage applied to the gap between the elelctrodes.
As described above, to prevent the deterioration of a laser medium gas or the descrease in laser oscillation efficiency, it is necessary to secure the prescribed insulation distance A between the enclosure 1 and the electrodes 5 in the convetional enclosure of a laser oscillator. Consequently, the conventional device is disadvantageous in that the miniaturization of the vessel 1 is restricted.